Conventionally, an image display device that forms a liquid crystal television and so on uses a surface light source device as a backlight device to backlight the liquid crystal display panel. Further, Patent Literature 1 has heretofore proposed a surface light source device that improves the contrast on the display screen of the image display device and turns off part of light depending on the state of image display on the display screen to reduce power consumption, and that is made thinner.
FIG. 1 shows one such surface light source device 100. Surface light source device 100 shown in this FIG. 1 is formed by combining in a matrix shape a plurality of light guide plates 103 on which light from LEDs (i.e. light emitting element) 101 is incident from side end surface 102, and is designed to turn on and off instantaneously each light guide plate 103 by turning on and off LED 101 provided to each light guide plate 103 and turn on and off illuminating light on a per light guide plate 103 basis.